How to simulate deformed metal
I've had some luck with this workflow, it still needs some polishing though.

The steps are as follows:


Choose a surface to deform(in this case the plane) 
Use cell fracture add-on to brake up the plane (Note that you should probably add a solidify modifier to it first).
Add a hook modifier to the plane object for every generated fracture (very important... and tedious). It can help to create a vertex group for each shard and then just go into weight paint mode loosely paint that shard onto the plane.
Turn off gravity in properties panel under the scene settings, this is vary important for the simulation to work properly (also because metal deformation isn't really effected by gravity it shouldn't be of much consequence).
If we are going to deform metal then we need something to deform it with. A sphere will work fine for know (any object will work). After you have an object then set it as a rigid body object in the physics, then check the animated check box:
Now we need to animate the sphere, Of course the animation part is all up to you (so long as the sphere intersects the plane). This is what I did, add a keyframe on the first frame in a high position, then add another keyframe on about frame 15 with the ball intersecting the plane.
Set the shards as rigid body objects.
Now it's time to run the simulation. Make sure that the shards, sphere and plane objects are all on the same layer(or at least visible), and press play. You will probably need to stop it around frame 12 or so before the dents get to deep and weird looking.


And here is the final result!

Hope this helps someone out there, it took me awhile to figure it out and it still needs polishing but I think that it has a lot potential.

blend file link: example blend